In the production of steel, for example, to avoid tying-up a primary melter, such as an electric furnace, an unfinished melt can be tapped from that melter into a ladle, carried by the ladle to a converting vessel, transferred from the ladle into this vessel where refining and finishing materials are injected directly into the melt to obtain rapid reactions and possibly alloying, transferred from this converting vessel into a ladle and carried by this ladle to a casting location where the finished melt is cast. This frees the primary melter for further use, more promptly than when that melter is used for finishing and alloying after producing the unfinished melt, but it involves a number of separate operations, which is obviously objectionable.
In the converter vessel, oxygen, possibly with Argon for cooling, can be injected directly into the melt to burn out carbon quickly with incidental reheating. Pulverized slag formers can be injected directly into the melt to obtain rapid reactions. It is also possible to inject pulverized alloying material into the melt to obtain rapid alloying.
However, the converter vessel must be a specialized piece of equipment, and because the melt must be carried in a ladle from the primary melter where the melt was formed, to the converter vessel, and in a ladle from the converter vessel to the casting location, the quality of the finished melt that is cast, is not as good as might be expected from the use of this practice.
In the ASEA-SKF process, which is the commercialized form of the invention disclosed by the British patent specification No. 1,112,876, published May 8, 1968, a single ladle is used for the refining and finishing operations. The unfinished melt is tapped from the primary melter into this ladle to free that melter for reuse, the ladle is moved into the field of an electric induction melt stirrer, the ladle being of non-magnetic construction, and the melt is stirred while possibly being subjected to evacuation by using an evacuating cover closing the top of the ladle, after which this cover is removed and replaced by a roof having electric arc heating electrodes so the temperature of the melt can be adjusted while alloying additions are dropped on the melt, the same ladle then being carried to the casting location. Sometimes, after alloying, an evacuating cover provided with an oxygen lance inserted in the melt through the melt's top surface, is used for vacuum-decarburizing the alloy additions.
Although this ASEA-SKF equipment permits a single ladle to be used throughout the refining and finishing operations, with the finished melt cast from this ladle into molds, it does not provide for the direct injection into the melt of gases, slag formers, deoxidizing agents, alloying material, etc., excepting for the lance possibly used during the vacuum-decarburizing of the alloy additions and which must be inserted through the top surface of the melt.
In the case of the refining converter of the first-described practice, it is usual to have injection nozzles in the bottom of the converter vessel and through which the gases or other materials can be injected into the melt when the melt is in the vessel, but this prohibits use of the refining converter otherwise than for the injection step.